The art is replete with greenhouses used to raise fruits, vegetables, and other plants, particularly during winter months. Currently, an estimated 250 acres of greenhouses are constructed in the United States each year. Conventional greenhouses are typically constructed with glass windows or translucent plastic sheeting, and suffer from a number of disadvantages. The cost of construction of a glass green house is relatively high, perhaps as much as $15-$25 per square foot. While the initial cost of a plastic greenhouse is somewhat lower, they require constant maintenance. The plastic sheeting currently available typically must be replaced every two to four years. The plastic is subject to being ripped or torn, and if this occurs during cold weather, the entire crop in the greenhouse could be lost.
Furthermore, conventional greenhouses are poorly insulated. While double panels of glass or plastic can be used, this increases the cost of construction and reduces light transmission. Thus heating requirements for conventional greenhouses are high, particularly in colder latitudes. Conversely, in warmer latitudes, air conditioning may be required because of the high solar gain.
Still another problem with conventional greenhouses is the lack of uniformity of the light. During winter months, sunlight enters the greenhouse at oblique angles. This results in low levels of light and plant-to-plant shading, which can cause uneven growth. This may require repositioning the plants to maintain uniform growth. Light diffusing films can be used to more evenly distribute the light, but they reduce the amount of light available to the plants.
Optical lighting systems are known for lighting buildings such as office buildings. For example, the multi-story office building known as 3M Austin Center located in West Austin, Texas includes an optical system comprising a first light reflecting means located outside the building, a vertical light transmitting roof panel and a second light reflecting means located inside the building. The 3M Austin Center optical system supports plant growth inside the building. However, the plants growing inside the building are grown for aesthetic purposes.
Other proposed multi-story office building optical systems comprise first and second light reflecting means and a sloped, light transmitting roof panel. However, such structures are not designed for the constraints of a commercial greenhouse. As a result, unduly large portions the aperture of the light transmitting roof panel is blocked by structures such as roof and optical supports and insulation.